The present invention relates to apparatus for classifying particles comprising a housing defining a classifying chamber, a feed duct for feeding particles to be treated and a feed duct for feeding classifying gas, both connected to the housing, a suction duct connected to the housing for transmitting gasborne fine particles resulting from a classifying operation, gas flow rate in the suction duct being maintained substantially constant, a discharge duct connected to the housing for discharging coarse particles resulting from the classifying operation, and a classifying rotor mounted in the housing and adapted to rotate at varied frequencies to select a classification standard particle size.
This type of classifying apparatus applies to the particles a floating force by the classifying gas and a centrifugal force by the classifying rotor at the same time, and discharges gasborne fine particles through the suction duct and coarse particles through the discharge duct. The classification standard particle size is changed or determined by changing the rotational frequency of the classifying rotor. Conventionally, this rotational frequency is changed manually, and therefore it is difficult to change, set and then maintain the rotational frequency, which makes it extremely difficult to carry out a desired classifying treatment.